Mistral metrics collector

Mistral users can benefit from flow and task metrics data. Mistral metrics collector would allow to provide real-time and historical data related to currently running / completed flows and tasks; actual and average execution time, optional statistical information (for example, rate of failed flows / tasks per day).
It would be helpful if metrics collector could enforce data filters based on privileges (admin can see all data, user / task owner can see only own data).
Data persistence layer can be implemented by integrating Ceilometer via REST API